Emergence of an Extensive Drug Resistant Citrobacter portucalensis Clinical Strain Harboring bla SFO-1 , bla KPC-2 , and bla NDM-1 .

Background: To explore the plasmid characteristics and transfer mechanisms of an extensive drug resistant (XDR) clinical isolate, Citrobacter portucalensis L2724hy, co-producing bla _SFO-1 , bla _NDM-1 , and bla _KPC-2 .
Methods: Species confirmation of L2724hy was achieved through 16S rRNA sequencing and Average Nucleotide Identity (ANI) analysis. Antimicrobial susceptibility testing (AST) employed the agar dilution and micro broth dilution methods. Identification of resistance genes was carried out by PCR and whole-genome sequencing (WGS). Essential resistance gene locations were verified by S1 nuclease pulsed-field gel electrophoresis (S1-PFGE) and southern hybridization experiments. Subsequent WGS data analysis delved into drug resistance genes and plasmids.
Results: The confirmation of the strain L2724hy as an extensive drug-resistant Citrobacter portucalensis, resistant to almost all antibiotics tested except polymyxin B and tigecycline, was achieved through 16S rRNA sequencing, ANI analysis and AST results. WGS and subsequent analysis revealed L2724hy carrying bla _SFO-1 , bla _NDM-1 , and bla _KPC-2 on plasmids of various sizes. The uncommon ESBL gene bla _SFO-1 coexists with the fosA3 gene on an IncFII plasmid, featuring the genetic environment IS 26-fosA3 -IS 26-ampR-bla _SFO-1 -IS 26 . The bla _NDM-1 was found on an IncX3 plasmid, coexisting with bla _SHV-12 , displaying the sequence IS 5 -IS 3000 -IS 3000 -Tn 2-bla _NDM-1 - ble-trpF-dsbD-cutA-gros-groL , lacking IS Aa125 . The bla _KPC-2 is located on an unclassified plasmid, exhibiting the sequence Tn 2-tnpR -IS Kpn27-bla _KPC-2 -IS Kpn6-korC . Conjugation assays confirmed the transferability of both bla _NDM-1 and bla _KPC-2 .
Conclusion: We discovered the coexistence of bla _SFO-1 , bla _NDM-1 , and bla _KPC-2 in C. portucalensis for the first time, delving into plasmid characteristics and transfer mechanisms. Our finding highlights the importance of vigilant monitoring of drug-resistance genes and insertion elements in uncommon strains.
Competing Interests: The authors report no conflicts of interest in this work.
(© 2024 Guo et al.)